Imagine if the WCML electrification was coming, but dieselisation was delayed. So you need a last hurrah of steam with a chunk more power. What would you do? My thoughts As a Duchess boiler seems to be as big as you can get (optimal length/diameter ratio) in the loading gauge, more boiler means smaller wheels. 8 coupled at 6' dia? This means faster wheel rotations, so roller bearings all round. But a duchess boiler is the limit of a single fireman, so my big idea is supplementary gas burners (which may also be handy to keep smoke down at termini). Gas-flow the heck out of it Also, with smaller wheels, cutting down reciprocating mass helps even more, so Caprotti valve gear. Would 1950s electronic technology permit more accurate valve events? How about poppet valves post WW2 experience? The basic premise is "how could you squeeze that bit more out of British- sized steam? Could you shrink a Chapelon compound down? Feed-water heaters?